There is known a liquid crystal display panel that comprises a TFT substrate on which thin-film transistor (TFT) elements are formed, a color filter (CF) substrate on which a color filter is formed, and liquid crystals placed between these two substrates. The following method is employed to fill liquid crystals into such a panel. A pattern is formed around a display area by using a seal material such as a thermosetting resin in order to hold the liquid crystals between the two substrates. This pattern has an injection port for injecting liquid crystals. After the seal material hardens, liquid crystals are filled through the injection port, and then the injection port is plugged. However, a lot of time is required for sealing the liquid crystals. As a method of solving such a problem, One Drop Filling (ODF) is known (See Patent Document 1).
According to ODF, a seal pattern is formed on one substrate by using a dispenser or by screen printing. Then, a predetermined amount of liquid crystals are dropped on the substrate on which the seal pattern has been formed. This substrate is aligned with the other substrate in a vacuum, to superimpose the two substrates and to press and stick them together.
According to the method of injecting liquid crystals, liquid crystals are injected after hardening of the seal material. As a result, a problem such as penetration of the liquid crystals into the seal material or flowing of the liquid crystals over the seal material does not occur. On the other hand, according to ODF, liquid crystals are dropped while seal material is in a soft state before hardening, and the substrates are attached and pressed to be bonded together by the atmospheric pressure while the seal material is hardening. Thus, since the liquid crystals in the panel are pressed by the two substrates, there occurs a phenomenon such as penetration of the liquid crystals into the seal material or overflow and leakage of the liquid crystals from the seal material, when the amount of the dropped liquid crystals is excessive. In this regard, Patent Document 1 describes a technique of preventing leakage of excessive liquid crystals by in-line control of an amount of the dropped liquid crystals and in-line recovery of the surplus.
Patent Document 1: Japanese Unexamined Patent Application Laid-Open No. 2002-107740